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Sedans Toyota Avalon 2008 Toyota Avalon
626 messages, Last post on Nov 24, 2009 at 6:42 PM
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Replying to: fin (Feb 28, 2007 12:06 pm)
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Replying to: captain2 (Mar 24, 2007 2:11 pm) Toyota adopted the DBW system to "protect the drive train", delay the onset of engine accelerating torque until a sequential downshift, following a full lift-throttle upshift, would be completed before the onset of engine torque rising. Not that other uses aren't made of DBW now that its there.
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Replying to: wwest (Mar 24, 2007 2:53 pm)
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Replying to: captain2 (Mar 25, 2007 1:38 pm) The brakes are used mostly for implementation of VSC functionality. Outside front brake for overstearing and inside rear brake for understearing. I suppose dethrottling the engine, especially with understearing, might be helpful, but again that can be accomplished via fuel cut. Obviously with DBW available it would be best to cut both intake airflow and fuel.
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Replying to: wwest (Mar 25, 2007 6:46 pm) |
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Replying to: captain2 (Mar 27, 2007 5:52 am) My 2001 Porsche 911/996 C4 has DBW and I have absolutely no complaints. The real problem is that Toyota/Lexus adopted the DBW system as a fix, solution, for another problem that seemingly could not be solved otherwise. They adopted the automatic transaxle upshift technique back at the beginning of the RX production run and that resulted in premature transaxle failures for those models. But the most obvious solution would have been to redesign the transaxle with a variable displacement ATF oil pump as Ford has done but that really is a major redesign whereas adopting the DBW system is relatively simple. And then asking those computer nerds to throw in a 2-3 second throttle opening delay while the transaxle is downshifting to the more appropreate gear ratios is another simple matter.
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Replying to: captain2 (Mar 27, 2007 5:52 am) Without such progress, the possibility of a 270-horsepower, two-ton vehicle travelling above 70mph while attaining over 30 mpg, would be unlikely. It seems clear that most consumers prefer the fruits of invention. The decades-old Crown Victoria design is being remaindered while its maker flounders toward the future with too little, too late. Some stumbles by manufacturers trying too much or too soon are less likely to be fatal to the organization.
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Replying to: gws (Mar 27, 2007 9:25 am) |
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Replying to: wwest (Mar 27, 2007 9:23 am) you're sure that is not more like - hey, these 'safety' systems sell like hotcakes, the government will be requiring them shortly anyway, so let's put in the DBW and then, we can address things like TS and engine braking issues more easily? Chicken or the egg. Nissans were selling just fine at the time of the RX intro with hellatious TS and correspondent engine braking issues without the DBW. Don't perceive that either the consumer or even the 'safety' nuts thought it was that much of a problem at the time (say 2002-03). The new Maximas/Altimas, though, this has 'disappeared' into electronic never-never land in combination with that CVT.
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Replying to: captain2 (Mar 27, 2007 10:57 am) The other issue is from an emissions startpoint, government, EPA, CARB, regulations. Using the SFI system to cut fuel and thereby reduce engine torque to accommodate these so called safety systems, VSC/Trac/BA/EBD/ABS/etc, was undoubtedly the most inexpensive method of accomplishing that task. But simply reducing the fuel flow but not closing the throttle to reduce airflow would quite certainly get the attention of those agencies. But, in your favor, totally, if the issue of engine RPM matching to road speed to reduce engine compression braking in the new Suzuki SX4 with manual transaxle is actually true then clearly a DBW system was required for that. |
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